Process for the production of reduced sulfur dyes

ABSTRACT

The dyeing behavior of a sulfur dyestuff, whether water soluble or water insoluble, is improved by electrolytic reduction. This reduction is performed in a cell in which the dyestuff is used as the catholyte. An ionic agent, such as salt or lye may be used to improve the conductivity of the catholyte. The dyestuff concentration in the cell ranges from about 5 to 50 percent by weight and 10 to 20 percent by weight is particularly effective. A porous clay diaphragm separates the anolyte and catholyte. The anolyte is for example, an aqueous lye or salt solution. The cathode is a material having relatively high hydrogen overvoltage, such as lead and alloy steels. The anode is a noble metal such as platinum or graphite. The catholyte is agitated during the reduction and its temperature is maintained from about 25* to 200* C. and preferably from 50* to 80* C. A current density of about 0.005 to 0.05 A./cm.2 is employed and preferably maintained from 0.01 to 0.04 A./cm.2. The reduction has an energy demand from about 0.5 to 1 kWh./kg. The termination of the reduction of water-insoluble sulfur dyestuff is determined by a spot analysis test. The end of the reduction of water-soluble sulfur dyestuffs is determined relative to hydrogen formation. After the electrolytic reduction has been terminated, the catholyte is stabilized by adding any of a number of suitable reducing agents.

ilniteei tates patent i rind et ai.

[ Feb. 8, 1972 [54] PROCES FUR THE PRQDUCTHQN 01F REDUCED SULFUR DYIES [72] Inventors: ll-liorst Frind; Christian iieid; Horst Aman,

all of Frankfurt (Main)-Fechenheim, Germany [73] Assignee: Caseila Farbwerke Mainkur Aktiengeseilschaft, Frankfurt (Main), Fechenheim, Germany [22] Filed: Feb.4,1970

[21] AppLNo: 8,733

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 19,027 1907 Great Britain ..204/73 OTHER PU BLICATIONS Chemistry of Synthetic Dyes Vol ll p 1083 pub. by Academic Press. lnc.. New York. I952 Primary ExaminerF. C. Edmundson AttrneyConnolly and Hutz [5 7] ABSTRACT The dyeing behavior of a sulfur dyestuff, whether water soluble or water insoluble, is improved by electrolytic reduction. This reduction is performed in a cell in which the dyestuff is used as the catholyte. An ionic agent, such as salt or lye may be used to improve the conductivity of the catholyte. The dyestuff concentration in the cell ranges from about 5 to 50 percent by weight and 10 to percent by weight is particularly effective. A porous clay diaphragm separates the anolyte and catholyte. The anolyte is for example, an aqueous lye or salt solution. The cathode is a material having relatively high hydrogen overvoltage, such as lead and alloy steels. The anode is a noble metal such as platinum or graphite. The catholyte is agitated during the reduction and its temperature is maintained from about to 200 C. and preferably from to C. A current density of about 0.005 to 0.05 A./cm. is employed and preferably maintained from 0.01 to 0.04 A./cm. The reduction has an energy demand from about 0.5 to l kWh/kg. The termination of the reduction of water-insoluble sulfur dyestuff is detemtined by a spot analysis test. The end of the reduction of water-soluble sulfur dyestuffs is determined relative to hydrogen formation. After the electrolytic reduction has been terminated, the catholyte is stabilized by adding any of a number of suitable reducing agents.

12 Claims, No Drawings PROCESS FOR THE PRODUCTION OF REDUCED SULFUR DYES BACKGROUND OF THE INVENTION It is well known that water-insoluble sulfur dyes become soluble and consequently acquire an affinity for fibers by a reduction process with sodium sulfide. Furthermore, it is known to impart an afiinity for fibers to water-soluble thiosulfuric acid derivatives of sulfur dyes by a reduction process with sodium sulfide. This reduction process, however, requires a considerable excess of the reducing agent, because the reaction takes place as an equilibrium reaction, for instance according to the following scheme:

The large amounts of sodium sulfide required for the reduction process involve serious difficulties in the purification of waste waters so that in view of the increasing demands made on the purity of the waters the dyeing with sulfur dyes becomes increasingly uneconomic.

SUMMARY OF THE INVENTION Surprisingly, it has now been found that water-insoluble as well as water-soluble sulfur dyestuffs may be electrolytically reduced while maintaining their stability and without the use of a protective gas. The electrolytic reduction according to the present invention is carried out in a diaphragm cell. The cathode materials used are preferably metals or metallic alloys with a high overvoltage of hydrogen, such as for instance lead or chrome-nickel steel. The aqueous dispersion or solution of the respective dyestuf'f represents the catholyte which is stirred or moved by pumping. In general, the content of electrolytes being present in the dyestuff as impurity, suffices in order to obtain the necessary conductivity of the catholyte. Should this not sufiice, the conductivity may be improved by the addition of salts or lyes. The concentration of the dyestuff to be reduced varies in the catholyte within a wide range, for economic reasons it should, however, not be inferior to percent by weight. Particularly good results are obtained within a range of concentration of -20 percent by weight. Ifdyestuff dispersions are employed that have a content of more than 30 percent, it might become difficult to stir and to pump the catholyte. In general, however, higher dyestufi' concentrations up to about 50 percent are more favorable, because thus an increase of the yield of current can be attained.

It is advisable to use as diaphragm a porous clay diaphragm. It contains the anolyte and separates the latter from the catholyte. The anolyte to be used is either an aqueous lye, such as soda lye 4N, or an aqueous salt solution, such as sodium sulfate solution 2N. The anode materials to be used are noble metals, such as platinum, or graphite. The electrolysis may be carried out at temperatures ranging from room temperature to about 100 C. The elevation of the temperatures causes, especially in the case of insoluble sulfur dyestuffs, an increase of the yield of current and lowers the bath voltage. Particularly favorable results with regard to the yield of current and a low evaporation are attained at temperatures ranging from 50 to 80 C.

The current density may be varied from about 0.005 to 0.05 A./cm. preferably from 0.01 and 0.04 A./cm. The bath voltage depends on the geometrical grouping of the electrodes, the tightness of the diaphragm, the conductivity of the solution or the dispersion and on the temperature and lies between 3 and 6 volt.

The process of the present invention may be applied to all sorts of water-insoluble or water-soluble sulfur dyestuffs.

If water-insoluble sulfur dyestuffs are employed, the end of the reduction is detemtined by means of spot analysis tests, whereas in the case of the electrolysis of water-soluble sulfur dyestuffs it becomes obvious from the beginning formation of hydrogen. vWith regard to the yield, in certain cases it has proved favorable to continue the electrolysis beyond this point. The expenditure of current for the electrolysis of the present invention is small and amounts from about 0.5 to l kWhJkg.

The dyestufi solutions that are electrolytically reduced according to the present invention are somewhat sensitive to air at its surface and form a protective skin. They may be stabilized by the addition of small amounts of reducing agents such as sulfites, thiosulfates, dithionites, thio urea dioxide, sugars, sodium formaldehyde sulfoxylate or sodium borohydride.

The solutions of sulfur dyestuffs that are electrolytically reduced according to the present invention may be either used directly for the dyeing or transfonned into dye pastes ready for dyeing. As remainder from the preparation they may contain a certain amount of elementary sulfur. Dyestufi' solutions that are completely free from sulfide are obtained by filtering off this sulfur or by employing dyestuffs or dye pastes that are free from sulfur. In the waste waters accumulating after the dyeing, no sulfide may be found.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are given for the purpose of illustrating the present invention. All temperatures are given in degrees centigrade.

EXAMPLE 1 Eighty grams lmmedialcarbon CBO (Color Index No. 53185) are dispersed in 400 cc. water and reduced at 60 in a diaphragm cell at a V4A cathode with a current density of 0.01 ampere/cmF. At a current strength of 2.2 ampere the reduction is tenninated after 3% hours as becomes obvious from the positive result of the spot analysis test. The thusly prepared sulfur dyestuff product may be employed as follows for the dyeing of cotton fabrics.

Thus, a cotton fabric is impregnated at 25 with a liquor containing 175 g./l. of the dyestuff solution electrolytically reduced according to the above description, 30 g./1. soda and 4 g./l. sodium hydrogensulfide, and then squeezed off so as to retain percent of its weight of the liquor. Subsequently, the thusly treated fabric is steamed for 40 sec. at rinsed and oxidized as usual with bichromate/acetic acid. Thus obtained is a black dyeing having good fastrress properties.

The waste waters accumulating in connection with the dyeing according to the above method only contain smaller amounts of sulfide than those accumulating in connection with the dyeing according to the usual methods.

EXAMPLE 2 Forty grams Immedialcarbon CBO (Color Index No. 53185) are dispersed in 400 cc. water and reduced at 60 in a diaphragm cell at a lead cathode with a current density of 0.01 ampere/cm At a current strength of 2.2 ampere the reduction is terminated after 2 hours as becomes obvious from the positive result of the spot analysis test. The thusly prepared sulfur dyestuff product may be employed as follows for the dyeing of cotton fabrics.

If the electrolysis is carried out twice the current strength, the reduction time is shortened by one-half.

A cotton fabric is impregnated at 25 with a liquor containing 375 g. of the dyestuff solution that is electrolytically reduced according to the above description, 30 g./l. calcined soda and 5 g./l. glucose, and then squeezed off so as to retain 80 percent of its weight of the liquor. Subsequently, the thusly treated fabric is steamed for 60 seconds at 105, rinsed and oxidized as usual with bichromate/acetic acid. Thus obtained is a black dyeing having good fastness properties.

The waste waters accumulating in connection with the dyeing according to the above process are nearly free from sulfide and contain only small amounts of reducing substances.

EXAMPLE 3 Forty grams of the green sulfur dyestufi' prepared according to the description given in US. Pat. No. 2,395,117, Example l, are dispersed as is described in Example 1 in 400 cc. water and reduced at 60 in a diaphragm cell at a lead cathode with a current density of 0.01 ampere/cm At a current strength of 2.2 ampere the reduction is terminated after 7 hours as the solved. The thusly prepared dyestuft' solution is stabilized by the addition of 4.1 g. sodium borohydridewhich is dissolved in 30 cc. sodium lye of 40 percent by weight. The thusly prepared dyestufi solution may be employed for the dyeing as spot analysis test shows. The reduced dyestuff solution may be follows Without the d n f fil -h lf r edtlcing agents- SlabiIiZCd by the addition of 1 percent sodium thiosulfate and A comm fabric is u p s d at 5 with a q r contamdirectly employed for the dyeing. Thus obtained are green mg 168 81 q h dyesmfisoluuon P p e" aeeordmg tel-he dyeings having good fastnessproperties. If such dyestuff above desenlmon and ,G 'e San and preparations are employed, the waste waters are only charged sflueezed off so 30 P r of. Weight 0f the w a very m extent liquor. Subsequently, the .thusly treated fabric is steamed for 40 seconds at 105", rinsed and oxidized as usual with bichro- EXAMPLE 4 mate/acetic acid. A blue dyeing having gooddye fastness properties is obtained with a good yield.

'Y $T 2 i ggf gfigss The electrolytic reduction of this invention may be con- So o y 3st e f o or u l ducted in an electrolytic cell of the general type described on Sulfur a sulfi'm P i' Fast Yenw page 63 of Introduction To The Chemical Process Industries by GWL, the constitution of which 15 described in Coll. C zech. Richard Stephenson; published by Reinhold Publishing Comm 153348 (1962)) are reduced f 60 m a Corporation, Copyright 1966. The aforementioned descripdiaphragm czell at a lead cathode with a current density of 0.02 tion however, is applicable only with respect to the general e te At a cunent Strength of ampere the f structure and not with respect to the particular materials and f e after e' hour as becomes obvlous composition for which the compositions of the present applie the beglflmng P hydrogen h fllusly cation are substituted. Some general considerations applicable tamed y e Solution 15 stemmed by the addmen 0f 1 P i" to this present application are also discussed in the section on cent by Weight of Sodlum Sulfite 1 Pereent y Welght Ofsodl- Electrolytic Cells on pages 60-68 of the aforementioned um formaldehyde sulfoxylate and 'f y employed text, with the exception of specific materials and composicording to one of the above described dyeing methods. It tions, which must be revised in accordance with the particuyields yellow dyeings having good fastness properties. l f thi present application,

The following table illustrates dyestuffs that have been elec- We claim: trolytically reduced under the given conditions according to l. A process for improving the dyeing behavior of sulfur the methods described in the above examples: dyestuffs comprising the electrolytic reduction thereof in an Content of the dyestufi Additives Tem- Energy in the to the pera- Current demand in catholyte catholyte ture density kilowattin percent in percent Cathode Anode in (anpere/ hour/kg. Dyestutf by weight by weight material materiel Anolyte 0. cm!) dycstufi Immedial-carbon CBO (01. No. 53186) 25.. Vanadium steel. Platinum- NaOH4N 80 0.02 0.2 Immedial New Blue FBL (C.I. No. 53470) 10.. ..do Graphite.. Ma1SO 2N 60 0.01 0. 2 Immediel Green GG (0.1. No. 53570)... 10.. Lead Platinum- NaOH4M 60 0.01 0. Immedial Yellow D (0.1. No. 53090) 10.. 0.2% NaOH Vanadium steel. ...do. Same........ 60 0.01 1. Immedial Fast Brown GGL (C.I. No. 53327). 15 Lead Graphite. NaOHZN 60 0.01 0.7 Immedial Fast Yellow GWL (the constltu- 10 ..do ..d0. Same........ 60 0.02 0.4

tion of which is described in 0011. Czech.

Chem. Comm. 27, 1533-48 (1962)).

Gll gen sullfutl dyestufi of U.S. Patent 2,395,117, 15 ..do....-...... Platinum. Na SO42N 80 0. 02 2 ram 8 Hydroso i Black B (0.1. No. 53186) 10 Vanadium steel... do NaOH4N 25 0. 02 1.0

HydrosolFastBlueB (0.1. No.53441). 15 g8j} Lead ..do Same........ 25 0.02 0.8

Hydrosol Fast Green 313 (0.1. No. 53572)..... 10 Vanadium steel. do ..do 25 0.01 1. 0

Hydrosol Fast Yellow G (thiosulfuric acid 10 do.... Graphite... NazSO42N 60 0.02 1. 0

from Immedial Fast Yellow GWL, constitution see above).

EXAMPLE 5 One hundred and twenty grams Immedialcarbon CBO are dispersed in 350 cc. water, admixed with 12 g. sodium hydroxide and reduced in a diaphragm cell at 60 at a lead cathode with a current density of 0.02 ampere/cm. At a current strength of 4.4 ampere the spot analysis test shows after 2 hours a positive result. Then the electrolysis is carried on for another 90 minutes. After switching off the current, the catholyte is admixed with stirring with 12 g. sodium hydroxide, 24 g. calcined soda and 18 g. glucose. The thusly obtained solution is ready for dyeing and shows a content of 22.4 percent of reduced dyestufi'.

EXAMPLE 6 Seven hundred and twenty grams of the aqueous paste of the dyestufi Immedial New Blue FBL (C.I. No. 53470) that is immediately formed in the preparation and has a dry content of 28 percent by weight, are dispersed in 485 cc. water and reduced in a diaphragm cell at 60 at a lead cathode with a current density of 0.02 ampere/cm At a current strength of 4.4 ampere the reduction is terminated after 5 hours.

By stirring the thusly prepared sulfur dyestuff product with 110 g. of a 32 percent sodium lye, elementary sulfur that has been introduced as impurity with the starting material is disionic aqueous suspension having a dye concentration of about 5-50 percent at a temperature of about 25l00 C., and a current density of about 0.005 to 0.05 A./cm. said electrolytic reduction is performed in an electrolytic cell having an anode disposed in an anolyte and a cathode having a high hydrogen overvoltage disposed in a catholyte and wherein said catholyte is separated from said anolyte by a diaphragm.

2. A process as set forth in claim 1 wherein said electrolytic reduction is performed in an electrolytic cell open to ambient atmosphere, said electrolytic cell having an anode disposed in an anolyte and a cathode disposed. in a catholyte, said catholyte comprises said. sulfur dyestuff and impurities therein, said catholyte is separated from said anolyte by a diaphragm, said diaphragm is porous clay, and said anolyte is an aqueous ionic solution.

3. A process as set forth in claim 2 wherein the conductivity of said catholyte is improved by the addition of an ionic agent and said ionic agent is selected from the group consisting of salts and lyes.

4. A process as set forth in claim 2 wherein, the concentration of said sulfur dyestuff in said catholyte is from about 5-50 percent by weight thereof.

5. A process as set forth in claim 2 wherein, the concentration of said sulfur dyestuff in said catholyte is from about 10-20 percent by weight thereof.

6. A process as set forth in claim 2 wherein said aqueous ionic solution consists essentially of an aqueous lye and said aqueous ionic solution consists essentially of an aqueous salt solution.

7. A process as set forth in claim 2 wherein, said anode is selected from the group consisting of noble metals and graphite.

8. A process as set forth in claim 2 wherein said sulfur dyestuff after being electrolytically reduced is stabilized by the addition of a reducing agent, said reducing agent is selected from the group consisting of sulfides, sulfites thiosulfates, dithionites, thio urea dioxide, sugars, sodium formaldehyde sulfoxylate and sodium borohydride.

9. A process as set forth in claim 1 wherein said cathode is a metal, selected from the group consisting of lead and alloy steels selected from the group consisting of steels alloyed with chrome, nickel and vanadium.

10. A process as set forth in claim I wherein, said catholyte is agitated during said electrolytic reduction.

11. A process as set forth in claim I wherein, the temperature of said sulfur dyestufi" during said electrolytic reduction is maintained approximately between 50 and 80 C.

12. A process as set forth in claim I wherein, the current density employed during said electrolytic reduction ranges approximately between 0.01 to 0.04 A./cm.. 

2. A process as set forth in claim 1 wherein said electrolytic reduction is performed in an electrolytic cell open to ambient atmosphere, said electrolytic cell having an anode disposed in an anolyte and a cathode dispoSed in a catholyte, said catholyte comprises said sulfur dyestuff and impurities therein, said catholyte is separated from said anolyte by a diaphragm, said diaphragm is porous clay, and said anolyte is an aqueous ionic solution.
 3. A process as set forth in claim 2 wherein the conductivity of said catholyte is improved by the addition of an ionic agent and said ionic agent is selected from the group consisting of salts and lyes.
 4. A process as set forth in claim 2 wherein, the concentration of said sulfur dyestuff in said catholyte is from about 5-50 percent by weight thereof.
 5. A process as set forth in claim 2 wherein, the concentration of said sulfur dyestuff in said catholyte is from about 10-20 percent by weight thereof.
 6. A process as set forth in claim 2 wherein said aqueous ionic solution consists essentially of an aqueous lye and said aqueous ionic solution consists essentially of an aqueous salt solution.
 7. A process as set forth in claim 2 wherein, said anode is selected from the group consisting of noble metals and graphite.
 8. A process as set forth in claim 2 wherein said sulfur dyestuff after being electrolytically reduced is stabilized by the addition of a reducing agent, said reducing agent is selected from the group consisting of sulfides, sulfites thiosulfates, dithionites, thio urea dioxide, sugars, sodium formaldehyde sulfoxylate and sodium borohydride.
 9. A process as set forth in claim 1 wherein said cathode is a metal, selected from the group consisting of lead and alloy steels selected from the group consisting of steels alloyed with chrome, nickel and vanadium.
 10. A process as set forth in claim 1 wherein, said catholyte is agitated during said electrolytic reduction.
 11. A process as set forth in claim 1 wherein, the temperature of said sulfur dyestuff during said electrolytic reduction is maintained approximately between 50* and 80* C.
 12. A process as set forth in claim 1 wherein, the current density employed during said electrolytic reduction ranges approximately between 0.01 to 0.04 A./cm.2. 